1. Field of the Invention
This invention relates to aircraft radio communications and more specifically to aircraft digital radio communication between an aircraft and an air traffic controller, or between aircraft.
2. Description of Related Art
In aircraft communication, there is a great deal of information which is communicated between an aircraft and an air traffic controller before and during each flight. Much of this is done by conventional analog VHF amplitude modulated (AM) radio voice communication. This tends to be very ineffident.
A number of 25 kilo Hertz (kHz) voice channels are currently allocated in the 118 megahertz (MHz) to 137 MHz in the conventional analog AM aircraft radio band. Each AM channel is allocated to an airport, with busier airports having several channels. Each radio tuned to an AM channel receives messages for all aircraft tuned to that channel. This is analogous to a "party line" service.
In congested terminal areas, the existing AM voice radio channels may become overloaded. There may not be enough time for all of the transmissions required by verbal communication. Also with the estimated expected increase in communication traffic, the problem increases.
An additional problem occurs when several pilots attempt to transmit over a broadcast channel at the same time, producing unrecognizable garble to a receiving unit.
Future aircraft communication requirements may be divided into 3 groups functional groups:
1) ground unit to aircraft unit Air Traffic Control (ATC) functions which are are Clearance Delivery (pre-taxi) messages, Taxi "Clearance" messages, Active Taxi Guidance messages and Direct Cockpit Alert messages. PA1 2) ground unit to aircraft unit surface traffic position reports that define other aircraft and ground vehicles near the aircraft, and
3) aircraft unit position reports for allowing the ground unit to perform surface surveillance.
Aircraft communications must be accomplished by means other than existing analog AM voice transmissions in order to meet future needs.
There are several possible communication methods employing different types of frequency allocations and access methods which may be employed for increasing the communication capacity.